Strip repository names from github URLs

[scottclowe]

At the moment, if a URL is given which directs to a github repository, may very will be of the format
https://github.com/scottclowe/dummy-package/archive/master.zip
which will currently result in the package name being detected as master.

Obviously this is undesirable since this will place the content into a badly named folder, but this may be a problem if multiple repositories are used with the same branch name for each (i.e. master), which would result in content potentially being overwritten when they are downloaded to the same location.

[scottclowe]

Of course, the same problem can be true of other content repositories, not just github.